The chicken core will support the specific aims of the program project by propagating on an annual basis chicken mutants of interest for the project, and by providing research materials as required by project participants. For the most part research material will be provided in the form of unincubated fertile eggs from currently maintained mutant stocks. Specified embryonic stages, hatchlings and adult tissue samples can be provided by prearrangement. Special crosses and additional mutant stocks can be incorporated into the chicken core on a space available basis.